docs/discover.adoc

@@ -24,34 +24,34 @@ include::includes/hand.adoc[]
 [[modes]]
 == Introduction ==
 
-This page describes the automatic server discovery schemes provided in
-NTPv4. There are three automatic server discovery schemes: broadcast,
-manycast, and server pool; which are described on this page. The
-broadcast scheme utilizes the ubiquitous broadcast or one-to-many
-paradigm native to IPv4 and IPv6.  The manycast scheme is similar
-to specifying to broadcast, but the servers listen on a specific
-address known to the client.  The server pool scheme uses DNS to resolve
-addresses of multiple volunteer servers scattered throughout the world.
-
-All three schemes work in much the same way and might be described as
-_grab-n'-prune._ Through one means or another they grab a number of
-associations either directly or indirectly from the configuration file,
-order them from best to worst according to the NTP mitigation
-algorithms, and prune the surplus associations.
+The NTPv4 *reference specification* supports three automatic server discovery
+schemes: broadcast, manycast, and server pool. However, NTPsec only supports
+the pool mechanism. For details on the reference specification,
+please see https://tools.ietf.org/html/rfc5905[RFC 5905].
+
+The pool scheme expands a single DNS name into multiple peer entries.
+This is intended for, but not limited to, the
+https://www.ntppool.org[NTP Pool Project], a worldwide set of servers
+volunteered for public use.
+
+The mechanism might be described as _grab-n'-prune._ Through one means or
+another, a number of associations are "grabbed" either directly or indirectly
+from the configuration file, and they are ordered from best to worst according
+to the NTP mitigation algorithms, and surplus associations are pruned.
 
 [[assoc]]
 == Association Management ==
 
-All schemes use an iterated process to discover new preemptable client
+Pool discovery uses an iterated process to discover new preemptable client
 associations as long as the total number of client associations is less
 than the +maxclock+ option of the +tos+ command. The +maxclock+ default
 is 10, but it should be changed in typical configuration to some lower
 number, usually two greater than the +minclock+ option of the same
 command.
 
-All schemes use a stratum filter to select just those servers with
-stratum considered useful. This can avoid large numbers of clients
-ganging up on a small number of low-stratum servers and avoid servers
+Pool discovery uses a stratum filter to select just those servers with 
+strata considered useful. This can avoid large numbers of clients
+ganging up on a small number of low-stratum servers and avoids servers
 below or above specified stratum levels. By default, servers of all
 strata are acceptable; however, the +tos+ command can be used to
 restrict the acceptable range from the +floor+ option, inclusive, to the
@@ -61,12 +61,9 @@ supplied using the methods described on the
 link:authentic.html[Authentication Support] page.
 
 The pruning process uses a set of unreach counters, one for each
-association created by the configuration or discovery processes. At each
+association created by the configuration or discovery process. At each
 poll interval, the counter is increased by one. If an acceptable packet
-arrives for a persistent (configured) or ephemeral (broadcast)
-association, the counter is set to zero. If an acceptable packet arrives
-for a preemptable (manycast, pool) association and survives the
-selection and clustering algorithms, the counter is set to zero. If the
+arrives for an association, the counter is set to zero. If the
 the counter reaches an arbitrary threshold of 10, the association
 becomes a candidate for pruning.
 
@@ -78,17 +75,17 @@ maximum. The pruning algorithm design avoids needless discovery/prune
 cycles for associations that wander in and out of the survivor list, but
 otherwise have similar characteristics.
 
-Following is a summary of each scheme. Note that reference to option
-applies to the commands described on the link:confopt.html[Configuration
-Options] page. See that page for applicability and defaults.
-
+Following is a description of the lool scheme. Note that
+reference to options applies to the commands described on the
+link:confopt.html[Configuration Options] page. See that page
+for applicability and defaults.
 
 [[pool]]
-== Server Pool Scheme ==
+== Pool Scheme ==
 
 The idea of targeting servers on a random basis to distribute and
 balance the load is not a new one; however, the
-http://www.pool.ntp.org/en/use.html[NTP Pool Project] puts
+https://www.pool.ntp.org/en/use.html[NTP Pool Project] puts
 this on steroids. At present, several thousand operators around the
 globe have volunteered their servers for public access. In general,
 NTP is a lightweight service and servers used for other purposes don't